Heat-treating solids



Dec. 5, 1950 P. H. ROYSTER HEAT-TREATING soups Filed July 19, 1945Convey /0 mom/0r Patented Dec. 5, 1950 HEAT-TREATIN G SOLIDS Percy H.Royster, Raleigh, N. (3., assignor to Pickands Mather & 00., Cleveland,Ohio, a copartnership Application July 19, 1945, Serial No. 605,861

2 Claims. 1

This invention relates to improved modes of heat-treating (includingdrying, decrepitating, roasting, calcining, indurating and similarthermal treatments) inorganic mineral solids such for instance as ores,ore materials, other metallurgical products, non-metallic raw materialssuch as fireclay, limestone and phosphate rock, and the like, and isparticularly concerned with apparatus for carrying out suchheat-treatments with improved heat economy.

This application contains subject matter in common with my copendingapplication entitled Process and Apparatus for Heat-Treating Solids,filed July 3, 1945, Serial No. 602,988.

More specifically, the invention relates toapparatus for and process ofindurating a continuously or intermittently moving stream of discretebodies or particles, particularly pellets, of moist oxidic iron orefines, at an elevated temperature of the order of 2000 F., while thesame flows by gravity through a pair of superposed thermally insulatedcommunicating treating chambers, in which process the stream of ore orore material is contacted with a treating gas, e. g., air, passed incounter-current heat-exchanging relation through said stream of pelletsor particles.

The problem of working up ore fines and other similar finely-dividedinorganic solids into objects of such size and structure as would makethem economically handleable in a metallurgical furnace such, forinstance, as a blast furnace, is very old and has received muchconsideration. Thus Mason (U. S. Patent No. 307,667), who proposed thatiron ore fines and the like be moistened with water (which might ormight not contain an added binder substance), formed into molded bricksor unmolded irregularly shaped small-masses and heat-treated in aquiescent state, suggested that the small masses be bedded in layers ofsolid fuel and the latter burned whereby to bake or burn the ore finesmasses in the intervening layers. Later, briquetting without or withsubsequent heat-hardening was proposed, as were sintering andnodulizing. As a variant to nodulizing and sintering, it was proposedthat such ore fines be moistened (without or with added bindersubstance) and formed into shapes or spheres (variously styled pellets"and g1omerules) which latter were to be dried and more or less baked butwithout excessive fusion of the mineral constituents of the ore. Onesuggested method of carrying out this scheme was to feed a stream of themoistened fines into -the upper end of a relatively long inclined rotarykiln at the lower end of which a high temperature was maintained by thecombustion of fuel therein; it was hoped that the moist fines would ballup at the initial stage of their travel through the kiln, and that theresulting spherical masses would be dried and eventually heathardenedduring their subsequent travel through the hot end of the kiln. Otherinvestigators, finding that the method just described wasunsatisfactory, in that the balls when dried became too fragile towithstand subsequent tumbling and as a result disintegrated badly,proposed that they be supported, in some obscure fashion, in a quiescentstate and without being subjected to breaking stresses while undergoinginduration; however, the proposals were not accompanied by any readilyunderstood procedure for efiecting the desired result.

It has been found that material disintegration of these pellets duringthe heating step may be avoided by accelerating the rate at whichtemperature of at least the outer laminae of the green" or raw, i. e.,untreated, pellets is raised from below 212 F. through drying to thattemperature level, e. g., 1650-2100 F. in the cases of most iron ores,at which a desirable degree of induration of the ore fines occurs, tothe end that such outer layers very rapidly are indurated. For effectingthis desirable result I cause a supported layer of the raw (that is tosay, moist and unbaked or untreated) p'ellets, initially at atemperature below 212 F., to be traversed by a mechanically propelledcurrent of a treating gas initially heated to a predetermined indurationtemperature for a period of time sufiicient not only to heat-harden theperipheral laminae of the pellets in the supported layer, but also toeffect thoroughgoing heating of the entire pellet body to induratingtemperature, and thereafter I cause the heat resident in theso-indurated pellets very largely to be transferred to the unheatedtreating gas which I use in the subsequent heating of the raw pellets.

In general, the process of the invention comprises the fOllOWiIlg steps:a mass of discrete pellets of oxidic iron ore fines, initiallysubstantially unheated and moist, is caused to move by gravity throughan upper treating chamber, a restricted conduit and a lower treatinchamber, the pellets filling the restricted conduit and also filling theupper and lower treating chambers save for upper and lower open spaces,in each treating chamber, contiguous with upper and lower bounding freesurfaces of the mass of particles therein, a current of treating gas (e.g., air), in-

.of a fuel introduced thereinto, from the combustion chamber to thelower open space of the upper treating chamber and thence to the upperopen space of the latter and to exhaust. In its travel-counter-currentto the pellets-through at least the major portion of the lower treatingchamber the initially substantially unheated treating gas is heated bycontact with heated pellets descending into the lower treating chamherby way of the aforesaid restricted conduit from the upper treatinchamber and the pellets so contacted are cooled to approximately theentrant temperature of said treating gas. During its passage through thecombustion chamber the treating gas, at least partially preheated, isfurther heated to about 2000 F. or the desired gas entrant temperature.

The thermally enriched treating gas, passed from the combustion chamberinto the lower open space of the upper treating chamber, at desiredtreating temperature, is forced through interstices between the pelletssubstantially filling said treating chamber and transfers heat to saidpellets, exhausting into the upper gas-collecting space at substantiallythe entrant temperature of the pellets fed to the apparatus. The pelletsin the lower portion of the upper treating chamber are heated thereby tothe desired treating temperature by heat transferred thereto from thetreating gas, and the heated pellets flow out of the upper treatingchamber through said restricted conduit and into the upper portion ofthe lower treating chamber in a heated state.

By suitable elongation and restriction of said restricted conduit, thepassage of preheated treating gas from the lower to the upper treatingchamber through the mass of pellets constantly filling said restrictedconduit is reduced to a negligible amount, the treating gas tending toexit from the mass within the lower treating chamber into the upper openspace of the latter and thence, by way of the communicating combustionchamber, to and through the lower open space of' the upper treatingchamber. To expedite this movement of the treating gas, I may partiallyexhaust gas from the upper open space of the upper treating chamber byany suitable exhaust means, so as to reduce the back pressure on thetreating gas passing from the combustion chamber into the lower portionof the upper treating chamber.

In firing" pelletized iron ore fines, initially containing moisture, atan indurating temperature of 2000 F., the total heat theoreticallyrequired to raise a gross ton of the raw (i. e., untreated) briquets orpellets to this temperature is 1,164,000 B. t. u. where about 80% of theheat (930,000 B. t. u.) represents the sensible heat of the 0.9 grosston of the resultant baked solids and only about is chargeable toevaporating the initially contained moisture. In view of these thermalrequirements, the economic necessity to discharge the solids from theapparatus at low temperature is five times as important as the meredrying and indurating of the solids. Accordingly, in carrying out myprocess, I prefer to discharge the dried and indurated pellets at areasonably close approach to ambient air temperature, e. g., near thedewpoint of the exhaust gases, and, equally important, to discharge thetreating gas at a, relatively low temperature (ideally, of course, atambient air temperature).

The invention will be described in greater particularity, with referenceto the accompanying drawing, in which the single figure is a schematicsectional elevation, taken on the vertical axes of the two heatingchambers, of one operable form of apparatus for carrying out the processor the present invention.

In the drawing, illustrating an apparatus for use in indurating pelletsof moist iron ore fines, are shown two similar heating chambers A and Barranged one above the other and connected by an elongated substantiallyvertical restricted conduit extending from the conical bottom of upperchamber B to and into the upper portion of chamber A and also by agas-heating means hereinafter to be described more particularly, andtheir necessary appurtenances.

In each of chambers A and B, l represents the substantially tubular sidewall, 2 represents the substantially conical roof and 3 represents thesubstantially conical bottom of the chamber. At least the lower portionsof chamber B and at least the upper portions of chamber A are thermallyinsulated as indicated by the refractory linings at 4 and 4. The bottoms3, 3 of the chambers are downwardly sloped at an angle greater than theangle of repose of the pellets.

6' represents a pellets-feeding chute positioned substantially at thevertical axis of chamber B and the apex of roof 2'. Chute 0' isprojected for some distance into the interior of heating chamber B whichprojected portion is illustrated at 40. Chute portion 40' and roof 2' ofchamber B are so designed that a bed I of pellets fed into B from 6occupies less than all of the upper in-- terior space of B, there beingan upper open space l8 between the free upper surface of bed I and roof2. 95 represents a substantially vertical elongated restricted conduitextendin from the apex of the conical bottom 3 of chamber B to, andprojecting for some distance into the interior of, heating chamber A,the projected portion being illustrated at 40: conduit 96 is formed ofor lined with refractory material. The lower end 40 of conduit 96 ispositioned sufiiciently below the roof 2 of chamber A as to insure themaintenance of an upper open space 30, in chamber A, between said roofand the upper free surface of a bed I of pellets in chamber A.

5 l 5 l represent relatively steeply sloping lateral walls dependingfrom side walls I, I, respectively, of chambers A and B. These lateralwalls serve somewhat to constrict beds I and I as these latter movedownwardly through A and B, the pellets of the beds rolling out beneath5|, 5| after they have passed the latter, to assume their normal angleof repose thereunder leaving beneath 5| an annular lower open space [8contiguous with lower free surface of bed 'I and under 5| a similar openspace 30'.

[9 represents a conduit communicatin between blower 22 and lower openspace I8 of chamber A. 23 represents a conduit communicating betweenupper open space l8 of chamber B and an exhauster 22' which latterdischarges to atmosphere.

Upper open space 30 (chamber A) is in gas communication with lower openspace 30 (chamber B) through assemblage C, composed of thermallyinsulated conduit 86, thermally insulated combustion chamber 10 andthermally insulated conduit 86.. 88 represents a fuel burner let intothe end wall of chamber 10 adjacent conduit 86,

and 26 represents a valved fuel supply pipe feedlng fuel to burner 98from a fuel source not shown.

Means for discharging treated pellets from heating chamber A consists ofa substantially vertical discharge chute 8, an adjustable discharge gate9 and a conveyor band III.

In operation, raw (i. e., moist, initially substantially unheated)pellets of iron ore fines are fed to the stockline of bed I of similarbut previously heat-treated pellets in chamber B. Restricted conduit 96is full of pellets, and chamber A likewise is full of pellets save forupper open space 30 and annular lower open space l8; the pellets in atleast the lower part of bed 1', in restricted conduit 96 and in thetopmost layers of bed I are hot, having been heat-treated (indurated) ina prior operation.

Air (the treating gas" in this case) initially substantially unheated,is forced by blower 22 through conduit |9 and annular lower open spacel8 (chamber A) and bed 1 to upper open space 39 (chamber A) in thispassage the air becomes preheated by transfer thereto of heat frominitially hot pellets resident in the upper portion of bed 1, and theselatter are correspondingly cooled.

The preheated air is forced from upper open space 30 (chamber A) throughconduit 86 into the space 3| within combustion chamber -10. A

gaseous fuel (e. g., blast furnace gas) is simulvtaneously introducedintospace 3| through burner 88 and there mingles with and is burned inthe preheated air; the amount of fuel so introduced and burned isadjusted to supply, by its combustion, only that amount of heatnecessary to raise the temperature of the air to the predeterminedtreating temperature (e. g., about 2000" F. in the cases of certainmoist iron ore fines pellets).

The so-heated air, containing gaseous combustion products but stilloxidizing in effect, is passed from space 3| through conduit 86' andinto annular lower open space 30 (chamber B) and thence through bed 1'and to upper open space l8 (chamber B). In its intimate contact with thepellets in the lower portion of bed I the initially highly heated airgives up heat to said pellets with the net result that the lowermostlayers of pellets have been heated substantially to 2000 F. by the timethey pass into conduit 96 and the air passes into the layers of pelletsin the upper part of bed 1' at a temperature intermediate its initialtemperature and the initial temperature of the raw pellets; as it passesthrough the upper part of bed 1 it further gives up heat in drying andheating the initially moist raw pellets, and correspondingly is cooled,so that it passes out of bed 1 into upper open space l8 at a temperaturesubstantially equal to or not far above the dewpoint of the air. The airis removed from upper open space I8 (chamber B) through conduit 23 bythe aid of exhauster 22' and from the latter is exhausted to atmosphere.

As will be appreciated, the rate at which indurated pellets aredischarged from the bottom of bed 1 through gate 9 determines the rateat which raw pellets feed onto the stockline of bed -'I' from ever fullchute 6. The selected discharge rate is determined mainly by threeconsiderations, viz., the desired heat economy, the desired powereconomy and the desired throughput. Where heat economy is all important,the rate of blowing and the rate of discharge of pellets are such as toinsure that the heat-treated (indurated) pellets moving out of bed I arecooled substantially to the entrant temperature of the air in lower openspace i9. Where a greater throughput at the expense of heat economy isthe more important, the heat-treated pellets can be discharged at afaster rate from bed 1 in which event they may pass out of the apparatusat a temperature more or less elevated a compared with the air entranttemperature, e. g., at F., 200 F., or the like. The rate of blowingpreferably is so adjusted that the temperature of the gas exhausted fromupper open space I8 (chamber B) is not unduly above the dewpointthereof.

As was mentioned hereinbefore, the operation may be and usually is socontrolled that pellets move as a continuous stream through theapparatus from 6 to ill. However, when the same is desired it ispossible to make the operation intermittent and to discharge and chargesmaller or larger batches. Thus, the discharge may be arranged to occurat intervals of a few minutes and to amount to a few inches only of bedi; or, it may be so arranged that a large fractional part of bed I isdischarged at one time and hence that a large fractional part of bed Idescends and is replaced by raw pellets.

The technical success of this process resides in the fact that arestricted conduit can be built large enough to permit a free flow ofparticles from the upper to the lower heating chamber without permittingleakage therethrough of any considerable amount of hot gas from lower toupper chamber. Many prior efforts to realize the successful heating andcooling of minerals in succession by causing an initially cool gas tofiow through a zone of the heated minerals (whereby to take up heattherefrom) and then to be heated and reintroduced into a bed of unheatedparticles have been technically unsuccessful because of the failure toprovide satisfactory means for removing the gas from the top of thelower column of minerals and, after being heated, for causing it tore-enter the upper chamber.

It is a matter of indifference, from the stand point of satisfactoryheat-treatment of the solids,

f whether the treating gas be forced thru A, C,

and B by means of a blower as at 22, or drawn through A, C and B bymeans of an exhauster as at 22, or both simultaneously.

It is to be understood that the apparatus is susceptible to considerablemodification without departing from the concepts of the presentinvention. Thus, assemblage C may be formed as a U-shaped thermallyinsulated conduit, and one may ,employ a plurality of burners 88 thereinor therealong. Rawpellets may be fed to the stockline of bed I ofchamber B by other feeding means than a gravity chute; also, they may befed to the bed by a plurality of chutes (or equivalent feeding means)spaced either over the area of conical roof 2' (so as to provide anirregular stockline comprising a plurality of conical piles of pellets)or about the upper periphery of side wall I. The bottom of chamber Abeing essentially cold, the lower open space therein may i be providedby other means than lateral wall 5|;

e. g., by a plurality of louver arches formed of structural metal. Infact, instead of lateral wall 5|, one may employ other means, e. g., aplurality of louver arches formed of refractory material or even ofheat-resistant alloy steel, to provide the necessary lower open spacefor intro duction of the heating gas into bed I at or adjacent thebottom of the latter. Any of the methods of feeding material into anddischarging the same from the treating chambers which are described inmy co-pending application Serial No. 602,988 referred to hereinbeforeare adapted to the present process: likewise, the present process issuitable for carrying out the several technical operations thereindescribed.

I claim:

1. Process of indurating in a shaft furnace discrete fluent bodies ofmoist iron ore fines, which comprises: establishing a gravitationallydescending column of previously indurated bodies of oxidic iron orefines, said column consisting of two gas traversable masses of thebodies disposed one above the other and communicating through anintervening portion of the column of restricted cross-sectional areacompared to the cross-sectional areas of said masses and illadapted tothe flow of gas therethrough; maintaining lower open spaces contiguousto lower free surfaces of each of said masses and gascollecting spacesof substantial extent above and contiguous with upper free surfaces ofsaid masses; charging a layer of initially substan-- tially unheated rawbodies onto the top surface of the upper mass and discharging a similarvolume of indurated bodies from the bottom of the lower mass therebymaintaining said columns height; passing a current of initiallysubstantially unheated air through the lower mass from the lower openspace thereof to and through the gas-collecting space thereof and into acombustion space spacially separate from said column thereby effectingheat exchange between the initially substantially unheated air and thebodies constituting said lower mass; thermally enriching the air in saidcombustion space, by introducing and burning a fluid combustibletherein, to an induration temperature below but approaching theincipient fusion temperature of the oxidic iron ore particlesconstituting said bodies; passing the thermally enriched air from thecombustion space to and through the upper mass from the lower open spacethereof to the gas-collecting space thereof thereby effecting heatexchange between the initially highly heated air and the bodiesconstituting said upper mass; so controlling the rate of flow of the airthat the same passes into the gas-collecting space above the upper massat a temperature above but close to its dew point; so controlling therate of discharge of indurated bodies from the bottom of the lower massthat the bodies are substantially cool as discharged; and so adjustingthe amount of fuel introduced into the combustion space with respect tochanges in the rate of flow of the air and in the 2. Process ofheat-treating in a shaft furnace.

discrete fluent bodies of moist mineral solids, which comprises:establishing a gravitationally descending column of previouslyheat-treated bodies of the mineral solids, said column consisting of twogas traversable masses of the bodies disposed one above the other andcommunicating through an intervening portion of the column of restrictedcross-sectional area compared to the cross-sectional areas of saidmasses and ill-adapted to the flow of gas therethrough; maintaininglower open spaces contiguous to lower free surfaces of each of saidmasses and gas-collecting spaces of substantial extent above andcontiguous with upper free surfaces of said masses; charging a layer ofinitially substantially unheated raw bodies onto the top surface of theupper mass and discharging a similar volume of heat-treated bodies fromthe bottom of the lower mass thereby maintaining said columns height;passing a current of initially substantially unheated air through thelower mass from the lower open space thereof to and through thegas-collecting space thereof and into a combustion space spaciallyseparate from said column thereby effecting heat exchange between theinitially substantially unheated air and the bodies constituting saidlower mass; thermally enriching the air in said combustion space, byintroducing and burning a fluid combustible therein, to a predeterminedheat-treating temperature; passing the thermally enriched air from thecombustion space to and through the upper mass from the lower open spacethereof to the gas-collecting space thereof thereby effecting heatexchange between the initially highly heated air and the bodiesconstituting said upper mass; so controlling the rate of flow of the airthat the same passes into the gas-collecting space above the upper massat a temperature above but close to its dew point; so controlling therate of discharge of heattreated bodies from the bottom of the lowermass that the bodies are substantially cool as discharged; and soadjusting the amount of fuel introduced into the combustion space withrespect to changes in the rate of flow of the air and in the rate ofdescent of the bodies that the temperature of the air passing into thelower open space of the upper mass is maintained at the aforesaidheat-treating temperature.

PERCY H. ROYSTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 915,534 Arnold Mar. 16, 19091,148,331 Olsson July 27, 1915 1,210,166 Hess Dec. 26, 1916 2,393,227Anderson Jan. 22, 1946 2,399,450 Ramseyer Apr. 30, 1946 2,417,049 BaileyMar. 11, 1947 I FOREIGN PATENTS Number Country Date 525,197 GreatBritain Aug. 23, 1940 OTHER REFERENCES Proceedings of the Blast Furnaceand Raw Materials Committee, vol. 4, (1944), pages 54-60.

1. PROCESS OF INDURATING IN A SHAFT FURNACE DISCRETE FLUENT BODIES OFMOIST IRON ORE FINES, WHICH COMPRISES: ESTABLISHING A GRAVITATIONALLYDESCENDING COLUMN OF PREVIOUSLY INDURATED BODIES OF OXIDIC IRON OREFINES, SAID COLUMN CONSISTING OF TWO GAS TRAVERSABLE MASSES OF THEBODIE3S DISPOSED ONE ABOVE THE OTHER AND COMMUNICATING THROUGH ANINTERVENING PORTION OF THE COLUMN OF RESTRICTED CROSS-SECTIONAL AREACOMPARED TO THE CROSS-SECTIONAL AREAS OF SAID MASSES AND ILLADAPTED TOTHE FLOW OF GAS THERETHROUGH; MAINTAINING LOWER OPEN SPACES CONTIGUOUSTO LOWER FREE SURFACES OF EACH OF SAID MASSES AND GASCOLLECTING SPACESOF SUBSTANTIAL EXTENT ABOVE AND CONTIGUOUS WITH UPPER FREE SURFACES OFSAID MASSES; CHARGING A LAYER OF INITIALLY SUBSTANTIALLY UNHEATED RAWBODIES ONTO THE TOP SURFACE OF THE UPPER MASS AND DISCHARGING A SIMILARVOLUME OF INDURATED BODIES FRM THE BOTTOM OS THE LOWER MASS THEREBYMAINTAINING SAID COLUMN''S HEIGHT; PASSING A CURRENT OF INITIALLYSUBSTANTIALLY UNHEATED AIR THROUGH THE LOWER MASS FROM THE LOWER OPENSPACE THEREOF TO AND THROUGH THE GAS-COLLECTING SPACE THEREOF AND INTO ACOMBUSTION SPACE SPACIALLY SEPARATE FROM SAID COLUMN THEREBY EFFECTINGHEAT EXCHANGE BETWEEN THE INITIALLY SUBSTANTIALLY UNHEATED AIR AND THEBODIES CONSTITUTING SAID LOWER MASS; THERMALLY ENRICHING THE AIR IN SAIDCOMBUSTION SPACE, BY INTRODUCING AND BURNING A FLUID COMBUSTIBLETHEREIN, TO AN INDURATION TEMPERATURE BELOW BUT APPROACHING THEINCIPIENT FUSION TEMPERATURE OF THE OXIDIC IRON ORE PARTICLESCONSTITUTING SAID BODIES; PASSING THE TERMALLY ENRICHED AIR FROM THECOMBUSION SPACE TO AND THROUGH THE UPPER MASS FROM THE LOWER OPEN SPACETHEREOF TO THE GAS-COLLECTING SPACE THEREOF THEREBY EFFECTING HEATEXCHANGE BETWEEN THE